The present invention relates to a crust breaker device for use to break crust in aluminum electrolysis cells, and including a driven unit with a bar, for instance a piston/ cylinder device with a piston rod, which is designed for axial movement basically in a vertical direction and a cutter bar or crow bar connected to a longer part of the bar and designed to be moved through the crust and to make a hole therein.
When producing aluminum with salt melt electrolysis, point feeders are used to supply additives such as aluminum oxide to the electrolysis cells. The additives are supplied batchwise to one or more points in the electrolysis cells by means of sophisticated supply equipment. Since the electrolysis bath of the cell is covered with a crust, crust breakers of the above type are provided to make holes in the crust to form the feeding points immediately before the dose of additives is supplied to the electrolytic bath.
The crust breakers usually are connected to the anode construction of the electrolysis cells, and to avoid short circuiting when the cutter bar is moved through the crust and into the electrolytic bath, the crust cutters are electrically isolated from the anode at connection points of each crust breaker (at least two points). However, to isolate the crust breakers from the anode is a cumbersome and time consuming task, since specially designed isolation structures, such as casings and discs for screws and nuts, have to be used, thereby demanding precise positioning and mounting. Besides, the isolation structure as such is expensive, and the possibility that the isolation structure will be damaged or defective is relatively large, whereby more or less current is led through the crust breaker, resulting in damage to the crust breaker and current losses. An isolation structure between the crust breaker and the anode according to known principles therefore represents an expensive solution.